Oblivion and Skyrim
Don't get me wrong - I didn't hate either of them. I just really couldn't get into them. And believe me, I tried. According to Steam I put 68 hours into Oblivion and 82 hours into Skyrim. So it's not like I played for five minutes and gave up.
I found the Oblivion leveling system to be frustrating. It isn't intuitive at all to have to focus on stats that don't make any sense for your character in the early game in order to maximize your effectiveness in the late game... and with the way enemies scale, it felt necessary to be min/maxing. I also didn't like how tedious the Speech skill was, how little it actually seemed to get you, and how horrifyingly bland all the characters were (which wasn't helped by the fact that the game's voice acting cast was so tiny that it wasn't uncommon to find the majority of an entire race/gender to be represented by a single person). The combat felt rather unbalanced, with the game seeming far easier for a caster - especially when working with custom-made spells. The story didn't feel particularly engaging either, which wasn't helped by the fact that the game seemed to do everything in its power to sidetrack you (which also made the main story plot seem far less urgent).
Skyrim I'll admit I had a much easier time getting into. A lot of the things I had a problem with in Oblivion seemed to be remedied. But it still suffered a lot from a plot that felt... inconsequential. With how hard the game tries to sidetrack you, it really takes all sense of urgency out of the story. The characters still felt rather bland and unmemorable to me, although at least the voice cast was noticeably larger. The scaling and combat felt far more balanced than Oblivion, although certain playstyles definitely felt far more cheap than others (Sneak/Archery... one-shot everything without ever being seen, even by enemies five feet away from you).
I'll admit I didn't actually beat either of them. I ended up just getting tired of them and moving on to other games. I don't think I'd call either of them bad games, I just felt like I was losing a war of attrition with them. The more I played them, the more tedious I found them to be, and the less engaged I got. It's not that I dislike RPGs, on the contrary they're actually among my favorite games... I just don't really care much for Elder Scrolls games, apparently. Though it could be because of fantasy fatigue. I'm really getting kinda bored with medieval weapons and armor, magic, orcs, and elves.